I have tried metal bobbins and several types of plastic ones, but the problem is that the bobbin "shuttle" or "hook", I am not sure what to call it, the mechanism that holds the bobbin itself. Anyway that whole mechanism needs to have a wider or bigger clip or something holding it from popping out. I believe it is a design flaw and not a defect that can be corrected with a new piece. When you go fast as you tend to do on a nice straight stretch the whole mechanism pops out and because miine is all plastic, the needle sews into it and makes little holes in it. Then you have to stop, and take it all apart and reposition it before you can resume sewing, at a much sloer speed. Very irriating.